Electrochemical Method For The Determination Of Ascorbic Acid

Chemistry modified electrodes are paid more and more attention to by the researchers in electronic chemistry and electro-analytic chemistry. With the help of the rich and varied supramolecule, organic substances, inorganic substance, polymer and biological substance and so on, it can make various design of modifying layers on the surface of electrode. It includes multivariate, multilayers, polycomponent, micronize, etc. That will make the detection more sensitive and more widely applied in analytic chemistry. And it has opened up a new path to research in Biosensor, combining the chemistry modifier on the surface of electrode and zymobiological reaction.Vc is considered as one of the most important elements that keep a person healthy. In the event of being short of it, a person may catch scurvy or lower the resistance to disease. Consequently it is quite significant to make quantitative analysis in the field of medicine and food.In this paper, modified electrode was used as the mian object in our research . We study the determinatiaon of vitamin C in fruits and vegetables by means of method of electroanalytical chemistry. There are four chapters.Chapter one is a summary of the theories and application in the determination of vitamin C by means of various electrochemical method.Chapter two A method for the determinatiaon of vitamin C by coulometric titration was developed. The titration was carried out in amixture of 1.0mol/L KI-1.0mol/LH3PO4(1:1V/V)when bromine wasgenerated at Vitamin C reacted with one mole of bromine with an value the anode of 2. The advantages of this method are simple, rapid and accurate.The method has been used for the determination of ascorbic acid in fruit juice drink and vegetables with satiafactory results.Chapter three Based on the fact that there are abundant Vc oxydase, the thesis aims to make out the cauliflower modified carbon paste electrode and make a comparison between that kind of electrode and carbon paste electrode. The results show that the anodic peak potential of Vc on carbon paste electrode is, Epa=0.46V while that on the cauliflower modified carbon paste electrode is, Epa=0.215V. And the anodic peak potential shifted negatively 245mV. The test indicates that cauliflowers have a outstanding effect on Electrocatal yticOxidation and the test is very sensitive, fast and selective. The results is satisfactory enough to be applied to determination of Vc.Chapter four mediator biosensor has emerged as the time requires in the past few years, in order to get rid of the disadvantages of the first biosensor which is based on oxygen electrode. The usual mediator in this kind of biosensor are terrocene and its derivative, quinone and its derivative. Among these the terrocene is better in reversible oxidation-reduction, as it is hydrophobic. That is to say, when applying to water system we can keep mediators away from falling off.Based on the theory that there are abundant Vc oxydase in the cauliflowers, this thesis is on how the author has made out the cauliflower modified carbon paste electrode. Compared with the performance of terrocene modified carbon paste electrode, a result is got like this: the anodic peak potential of Vc in terrocene modified carbon past electrode and in cauliflowers areEpa=0. 20V, Epa=0. 0V apparently. That suggests that the terrocene plays an obvious role in electric catalysis of Vc. Besides, the latter is better than the former. And the sensitivity has greatly improved. It is quite easy to tell the anodic peak of terrocene and that of Vc. In conclusion, it is satisfactory to test the content of Vc in fruits, vegetables, and drinks by the way of differential-pulse voltammogram.